Sei Yoshida Dep. of Phys., Osaka Univ.

Double beta decay 世界の現状・将来計画

CANDLES実験

Two decay modes are usually discussed for ββ decay: ① 2νββ decay : (A,Z) → (A,Z+2) + 2e- + 2νe

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W

W

e-

e-

νe

νe

W

W

e-

e-

νe

νe = νe

mν

allowed by the Standard Model. already observed in more than 10 isotopes. Lifetimes ; τ > 1018 yr

② 0νββ decay : (A,Z) → (A,Z+2) + 2e-

process beyond the Standard Model. Lepton number violation non-zero neutrino mass Majorana particle

not observed yet, except for the KKDC claim. predicted lifetimes ; τ > 1026 yr

Dirac or Majorana particle 0νββ discovery Majorana

only practical technique to investigate the Majorana nature of ν

∆L ≠ 0 (Lepton number non-conservation) Leptogenesis ? B-asymmetry in the Universe

See-Saw mechanism ? mν = mD

2/MR << mD

Mass hierarchy/Mass scale Normal or Inverted ?

Effective Majorana mass

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Inverted hierarchy

Normal hierarchy

∆m2atm = ∆m2

31 = (2.3 ± 0.2 ) 10-3 eV2

∆m2sol = ∆m2

12 = (7.9 ± 0.3) 10-5 eV2

(Next generation) 0νββ decay experiment; sensitivity target ~ a few tens meV.

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Sum electron energy / Qββ

S.R.Elliot and P.Vogel, Ann. Rev.Nucl.Part.Sci.52(2002)115.

0νββ decay ; peak at Qββ

2νββ ;

continuum to Qββ end point

two electrons from vertex production of daughter isotope

FWHM = 5% @ Qββ

0νββ/2νββ = 10-6

2νββ

0νββ

The shape of the two electron sum energy spectrum enables to distinguish the two different decay modes. Good energy resolution.

Neutrino mass sensitivity ;

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<mν> ∝ T0ν-1/2 ∝ ( NBG・∆E / M・Tlive )1/4

M・Tlive : exposure (kg.yr) massive isotope

NBG : background rate @ Qββ (events/keV/kg/yr)

reduce radioactivity go to underground cosmogenic BG

∆E : energy resolution (keV) Good energy resolution

assuming background is increased by M・Tlive scaling

Large mass Natural abundance/Isotopic enrichment

Low background Radiopurity for source, detector materials Large Qββ against natural RI

Shieldings Underground operation against cosmo-genic Slow 2νββ rate (high energy tail)

Good energy resolution can separate 0ν/2ν spectra minimize Qββ analysis-window

And others for Tlive... easy to operate (demonstrated technology) July 22nd, 2012 7

<mν> ∝ T0ν-1/2 ∝ ( NBG・∆E / M・Tlive )1/4

Nuclear sensitivity large 0νββ decay rate

For Detector

Decay rate (observable quantity) ;

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T0ν-1 ~ G0ν(Qββ,Z) |M0ν|2 <mν>

2

G0ν : phase-space factor |M0ν|2 : Nuclear matrix element

only theoretical calcurate with nuclear models Uncertainty ; factor of ~2

<mν> : (effective) Majorana mass <mν> = |∑Uei

2 mi| Uei ; (complex) neutrino mixing matrix

assuming light neutrino exchange (Mass term)

48Ca 48Ti 4.271 0.187

76Ge 76Se 2.040 7.8

82Se 82Kr 2.995 2.8

96Zr 96Mo 3.350 9.6

100Mo 100Ru 3.034 11.8

116Cd 116Sn 2.802 7.5

124Sn 124Te 2.228 5.64

130Te 130Xe 2.533 34.5

136Xe 136Ba 2.479 8.9

150Nd 150Sm 3.367 5.6

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Isotopes Q (MeV)

Abundance (%)

Favorable isotopes

Phase space factor

208Tl Q-value (5.0 MeV)

214Bi Q-value (3.3 MeV)

208Tl γ (2.6 MeV)

Nuclear matrix elements only theoretical calcurate with nuclear models Uncertainty ; factor of ~2 Model dependent Measuring 2νββ decay rate check reliability of calcuration

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A. Dueck, et al., PRD 83 (2011) 113010

Important to observe 0νββ by several Isotopes !

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Published by part of collaboration members H.V.Klapdor-Kleingrothaus, et al., Mod. Phys. Lett. A21(2006) 1547

This result was a controversial matter

Heidelberg-Moscow experiment ~ 11 kg of enriched 76Ge

Fitted by 6 gaussians + linear BG

Excess events at Q-value 28.75 ± 6.86

Claimed significance ; 4.2 σ Results

T1/2 = 2.23 +0.44-0.31x 1024 year 〈mv〉= 0.32 ± 0.03 eV

BG candidate

For ex. 206,207Pb(n,γ)

Source = Detector (Calorimetric)

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Source ≠ Detector (Tracking)

検出器技術が多様化 とりあえず大雑把に分類

Ionization GERDA (76Ge) MAJORANA (76Ge) COBRA (116Cd)

Bolometers CUORE (130Te) LUCIFER (82Se) ZnMoO4 (100Mo) AMoRE (100Mo)

Scintillator KamLAND-ZEN (136Xe) SNO+ (150Nd) CANDLES (48Ca)

Liquid Xe EXO (136Xe) XMASS (136Xe)

Tracking + Calorimeter

Super-NEMO (82Se) MOON (100Mo)

DCBA(MTD) (150Nd) NEXT (136Xe)

TPC

Requirements for Detectors Large mass Low background Good energy resolution And others for Tlive.. Various isotopes

EXO-200 (first phase) 200 kg enriched 136Xe (80%) ; Liquid TPC Operating (as of early 2011) underground Probe Majorana mν ~ 100 meV scale Confirm or refute KKDC result Demonstrate feasibility of ton-scale xenon experiment

“Full-EXO” (second phase) 1-10 ton-scale enriched 136Xe 0νββ experiment Probe Majorana mν ~ 5-20 meV scale R&D effort for “Ba-tagging” of 0νββ daughter nucleus as a means of radioactive background rejection

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Constructed by radio-pure materials Multi-site events reduction

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Slide : J.Farine in Neutrino2012

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Slide : J.Farine in Neutrino2012

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Crystals of TeO2 are cooled to ~ 10 mK inside a dilution-refrigerator cryostat.

Cold crystals have such small heat

capacities that single interactions produce measurable rises in temperature

Temperature pulses are measured by

thermistors glued to the crystals A pulse’s amplitude is proportional to

the energy deposited in the crystal High natural abundance (~ 34%),

so enrichment isn’t necessary. Good Q-value @ 2528 keV:

above natural γ energies large phase space

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Ge detectors in the Liquid Ar Scintillator. LAr works as active shielding.

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Concept works : diodes enriched in 76Ge in liquid argon (Lar) @ LNGS GERDA is running and taking data Phase-I

statistics: 1.11.2011 – 21.5.2012 ( enrGe exposure 6.10 kg yr ) systematics: blinding 2019 – 2059 keV background index (BI) : 0.020 +0.006 -0.004 cts/( keV kg yr ) [68% coverage] LAr: 42Ar (42K) activity determined: (93.0 ± 6.4) µBq/kg 76Ge T1/2(2νββ) = ( 1.88 ± 0.10 ) 1021 yr all results are preliminary !!!

Preparations for Phase II progressing well:

increase in mass by add. ~20kg (26+ BEGe) & BI = 10 -3 cts/( keV kg yr ) 9 crystals pulled – milestone completed successfully !!

complete Phase I and start Phase II in early 2013

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CRESST-II at LNGS for DM search (CaWO4) e/γ backgrounds will produce scinti. Light WIMP induced recoils, little or no light.

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Scintillating bolometers to recognize the α-induced background thanks to the readout of the scintillation light Array of 36 ~ 44 enriched (95%) Zn82Se crystals. Expected background in the ROI (2995 keV) is

∼ 3~6 x 10-3 c/keV/kg/y Energy resolution ∼10 keV FWHM

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The α-induced background is recognized:

1) the decay time of the scintillating signal 2) the different scintillation yield between

α and γ/β particles (the “usual” light Vs Heat scatter plot)

LUCIFER will be located in CUORICINO (now CUORE-0) cryostat, once CUORE-0 will finish their data taking (2015)

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Energy & angular correlation Mechanism of 0νββ

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Slides : F. Piquemal in Neutrino2012

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Slides : H. Iwase in DBD11

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ここからは、時間の許す範囲で

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0νββ by 48Ca isotope Highest Q-value (4.27MeV) Low background γ-ray ; 2.6 MeV (208Tl) β-ray ; 3.3 MeV (214Bi)

Background Free検出器を目指す

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CaF2(pure) scintillator Transparent Crystal Long attenuation length (>10m@350nm) ββ decay source = detector Wave length Shifting mechanism

CaF2(pure) ; 280nm emmision WLS (bis-MSB) ; 420nm emission

Liquid scintillator

4π active shield

Large photomultiplier tube

Signals from both scintillators are detected simultaneously

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CANDLES CAlcium fluoride for studies of Neutrino and Dark matrters

by Low Energy Spectrometer

CaF2(pure)

Liquid Scintillator (Veto Counter)

Buffer Oil

Large PMT

CANDLES III 3m diameter × 4m height (water tank)

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Lab D

Super Kamiokande

KamLAND

CANDLES

Kamioka Lab. Map

4m 3m

CANDLES III

XMASS

GDZOOKS!

Data taking from June, 2012

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Main detector CaF2 scintillators (305kg)

PMTs 13 inch (side) ; x 48本 17 inch (top & bottom) ; x 14本

Liquid scintillator acrylic tank (2m3)

Light-pipe system Gain ×1.8

Event reconstruction Under developing the reconstruction tools

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Enrichment of ββ isotopes 136Xe, 100Mo, 76Ge, 82Se, 116Cd … : Available 48Ca, 150Nd ; Difficult (limited small amount)

Technologies for 48Ca Enrichment Gas diffusion × Gas centrifuge × Chemical process ○

Isotope enrichment by Crown-Ether

Crown-ether rings adsorb Calcium ions For calcium, 40Ca adsorption in crown-ether is slightly prior

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No gaseous compound for Calcium

o o

o

o o

Crown-Ether

40Ca ion

Enrichment by crown-ether Crown-ether rings adsorb

Calcium ions For calcium, 40Ca adsorption in

crown-ether is slightly prior

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fixed flow rate by pump

２. Ca solution CaCl2

1. Crown-ether resin packed in column of 8mmf ×100cm

３. Sampling

1m glass column

Migration length = 1m 20m 200m

Enriched 48Ca

Natural Ca

40Ca : captured

o o

o

o o

Crown-Ether

40Ca ion

Isotope Enrichment with Longer Migration Time (Length)

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~ 7hours 1m migration length

~ 70hours 20m

~ 250hours 200m

Amount of Enrichment by Crown Ether

longer longer

larger (volume of Ca) higher (isotopic ratio)

larger higher

Isotope Effect by Crown-ether max: 0.0026

Natural isotopic ratio = 0.0019

・The longer migration time(length) = the larger volume and the higher isotopic ratio ・48Ca enrichment → next CANDLE system

Isotope Effect (Enrichment Effect)

CANDLES Series

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CANDLES III

3.2kg×96 crystals 305kg

4.0%(Req.) 0.01 0.26

0.27/year 0.5 eV

Next CANDLES

2 ton 2.8%(Req.)

<0.2 ~0.1

< 0.3 /year 0.05

Crystal

Total Mass Energy Resolution

2νββ 212Bi,208Tl

Expected BG <mn>

Measurement at Kamioka Lab. sensitivity 0.5eV

CANDLES III 2012 2013 2014 2015

48Ca enrichment Not funded …

Next CANDLES

2% 48Ca and cooling system for CaF2

48Ca enrichment ; 1 crystal Cooling system for CaF2

Several experiments at ~ 100 kg are running and prepared. Sensitivity : KKDC claimed region 50 – 100 meV

To explore inverted hierarchy region Required ;

Several isotopes Several method ,for ex.

Scintillating bolometer (BG reduction) Tracking (Understand 0νββ mechanism)

CANDLES III at Kamioka Lab.

300kg of CaF2(pure) scintillators Pre-measurement for performance test Expected sensitivity : 0.5 eV for <mν>

R&D (for next CANDLES) Enriched 48CaF2(pure) scintillators

+ Cooling system for CaF2(pure) Sensitivity : ~0.2 eV~0.05eV

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